Modern communication systems allow individuals to stay in communication as they move about. The most widespread and popular device for this is the cellular telephone, which allows people to communicate verbally with each other. Unfortunately, cellular telephones are associated with specific users. Thus, different people cannot use the same cellular telephone and all be associated distinctly with it, which would aid in billing and placement of calls to and/or from the cellular telephone.
There also exist a variety of other communication devices to which people need access as they move about, such as voice over Internet protocol devices in enterprises. These devices typically suffer from the same drawback previously discussed for the cellular telephones—the inability for different people to use the same telephone and be distinctly associated with the telephone.